interface Options {
    timer?: number
}
 
export class Updater {
    oldScript: string[] //存储第一次值也就是script 的hash 信息
    newScript: string[] //获取新的值 也就是新的script 的hash信息
    dispatch: Record<string, Function[]> //小型发布订阅通知用户更新了
    constructor(options: Options) {
        this.oldScript = [];
        this.newScript = []
        this.dispatch = {}
        this.init() //初始化
        this.timing(options?.timer)//轮询
    }
 
 
    async init() {
        const html: string = await this.getHtml()
        this.oldScript = this.parserScript(html)
    }
 
    async getHtml() {
        /**这里可以根据部署到生产环境来做判断 */
        const html = await fetch('../../dist/index.html').then(res => res.text());//读取index html
        return html
    }
 
    parserScript(html: string) {
        const reg = new RegExp(/<script(?:\s+[^>]*)?>(.*?)<\/script\s*>/ig) //script正则
        return html.match(reg) as string[] //匹配script标签
    }
 
    //发布订阅通知
    on(key: 'no-update' | 'update', fn: Function) {
        (this.dispatch[key] || (this.dispatch[key] = [])).push(fn)  
        return this;
    }
 
    compare(oldArr: string[], newArr: string[]) {
        const base = oldArr.length
        const arr = Array.from(new Set(oldArr.concat(newArr)))
        
        //如果新旧length 一样无更新
        if (arr.length === base) {
            this.dispatch['no-update'].forEach(fn => {
                fn()
            })
        
        } else {
            //否则通知更新
            this.dispatch['update'].forEach(fn => {
                fn()
            })
        }
    }
 
    timing(time = 10000) {
         //轮询
        setInterval(async () => {
            const newHtml = await this.getHtml()
            this.newScript = this.parserScript(newHtml)
            this.compare(this.oldScript, this.newScript)
        }, time)
    }
 
}